As is well known, graft polyblends of rubbers with various vinylidene polymers have advantages in providing compositions of desirable toughness, chemical resistance and good formability. ABS polyblends have proved particularly advantageous in many applications, and modifications of such ABS polyblends include the substitution of alkyl acrylate esters for a portion of the vinylidene monomer components, variations of the ratio of styrene-type and acrylonitrile-type monomers and the use of saturated rubbers such as acrylate rubbers as the substrate for the graft.
In U.S. Pat. No. 3,509,238 granted Apr. 28, 1970 to Aubrey and Jastrzebski, there is disclosed and claimed an ABS-type polyblend containing graft copolymers having distinct degrees of grafting to provide a highly desirable balance of properties, the lowly grafted polymer apparently tending to cluster and simulate a larger particle size graft copolymer to provide a very high degree of impact resistance. In U.S. Pat. No. 3,509,237 granted to Norman E. Aubrey on Apr. 28, 1970, there is disclosed and claimed an ABS-type polyblend wherein there are graft copolymer particles of relatively small size and graft copolymer particles of relatively large size.
The concepts of the aforementioned applications have been widely employed in commercial compositions. In the use of the concept of the latter of the above mentioned applications, the large particle component has been provided by a mass/suspension polymerization process and the smaller particle component has been provided by an emulsion polymerization process. There has been a desire to prepare both components in a single reaction by the same polymerization process in an effort to minimize cost. In such efforts utilizing an emulsion process, there has been encountered considerable difficulty because of the tendency of agglomerated latices to be unstable during the grafting reaction and also because of the desirability of controlling the amount of grafting upon the rubber components of different particle size.
It is the object of the present invention to prepare ABS polyblends having grafted large agglomerated rubber particles only that are free of hard spots and have superior toughness for pipe and molding applications.
It is a further objective of this invention to provide a process that will prepare such ABS polyblends having larger rubber particles by emulsion polymerization only.
U.S. Pat. No. 3,663,656 relates to a process for grafting large agglomerated rubber particles in latices but requires that small rubber particles must be grafted first to stabilize such latices before the large agglomerated rubber particles are added to the latex and grafted. This process requires two steps to graft larger particles increasing costs by the use of large amounts of small rubber particles and the additional steps involved. An all emulsion process was needed to produce ABS polyblends having only large grafted rubber particles in the range of 0.30 to 1.0 microns.
It has now been discovered that agglomeration larger rubber particles that provide greater toughness in ABS polyblends, can be grafted in latices that have been stabilized with oligomeric surfactants.